Android: If you've ever tied a string to your finger or left yourself a sticky note for all-day reminders, Toastr is a small app that will move those reminders to your phone. Just tell it what you want to remember, and it will give you a small, customizable popup every time you unlock it.

That's pretty much all there is to Toastr—it's simple, useful, and effective. Just tell it your message and whether you want it to last 1.5 seconds or 3 seconds, and you're done. The $0.99 pro version also lets you customize things like the position of the popup, size, and color of your text, if you want to get a little more creative.